Research and Development Laboratories
of the
Portland Cement Association
RESEARCH DEPARTMENT
Bulletin 83
Studies of 'Salt' Scaling
of Concrete
By
George Verbeck and Paul Klieger
June, 1957
Chicago
Authorized Reprint from
Highway Research Board Bulletin No. 150
January, 1956
Studies of "Salt" Scaling of Concrete
GEORGE J. VERBECK, Manager, and
PAUL KLIEGER, Senior Research Engineer,
Ap|,, >rch Section, H»- ,< ■ ir< ■:■. in 1 Development i
• rid Cement A
rd of air-. . rete pav
lent, However, the n,» vhlch de-icers
more, (hi-rc Li I i
ird
Although h»
i Km
.111(1 CHI'
I
I
, .l-i !>♦• ol '•*•
• I
A
in, the m
>i>. Mm
in.lllv h»
• tea
i
llll:
npletely I I
All |pj| :
-hown in le a
a*K rebates *
<hed in th< uir-dn
1
■
^tJA%
y%%
II *r
16% ^s^*^
u / J^
__ — - — -""o*
NaCI
Non A /E
NaCI
- A /E
?\<
■
4%^-^
_ — ^^82
.
16 %>
100 ,S0 *» b0 ,00 ,50 200
Number of Cycles of Scaling Test
Figure 1. Effect of amount of de-icer on surface scaling on non-
K 1T ~o nt £" lned 8nd air ' entrairied concretes. Scale Test Procedure
Thmm solution refrozen on slab surface. Aggregates. Elgin,
Illinois sand and fcau Claire, Wis. crushed gravel (1-in. top size)
ens: 3 by 6 by 15-in. slabs cured continuously moist for 31
days prior to test. Cement Content: 6 sacks per cu yd. Slump-
I 12 to 3 1,2 in. Air Contents: Non A/E - 2-2 percent, A/E - 7.4
percent.
to use inundated with a known amount of water. Excess water was drawn off and
weighed immediately prior to mixing the concrete
entrame r d a concre!e S01 reSl " * S ° 1Uti ° n WM a<Wed at the ™™ T When P re P a »ng the *,-
sodium rM^ USed ln th ^ se l scali "g *»* were commercial flake calcium chloride,
soaium chloride, urea, and ethyl alcohol.
Fabrication of Specimens
Each batch contained 1. 30 cu ft of concrete. Batches were mixed for 2% minutes in
an open-tub mixer of 1%-cu ft capacity. A slump test and an air content determination
by the pressure method were made on each batch of concrete.
Generally, two specimens were made for a particular test condition. In a few cases,
three specimens were made. In all cases, these companion specimens were made on
different days.
The specimens used in the scaling test were slabs 3 in. in depth and 6 by 15 in. in
area. These slabs were cast in watertight steel molds, the molds were filled in two
5 -
c
"5
u
to
CO
CD
Calcium Chloride £
/
/
Non%50 Cycles
Sodium Chloride
t/Von % 25 Cycles
*/e 200 Cyc/es
*/E y SO Qt/c/es
ro
u
CO
CD
O
E
c
"(0
u
n if)
Z o
i
o
5
1 7 1 f T
, * , Urea
4
/ \Non A / E
\f*\ \ 50 Cyc/es
3
Z
1
i
11 \ Y
v \ \
^OOCue/es^^^
,<T7 0^^
^%-50 Cyc/es
E_th y I Alcoho l
A/on a /e
50 Cyc/es .
7-,
Ye -50 Cyc/es
8 \Z 16
Solution Concentrations - % by weight
Figure 2. Effect of amount of de-icer on surface scaling (test pro-
cedure No. 2 - thaw solution refrozen).
1 //
jr
.
. r
,-..c
' ...
B .
/
/ / fti*4f [g y '"'
.
-
Ifcl.
-
Curing Conditions
Companion specimens were subjected to two different sets of curing conditions:
1. Continuously moist cured at 73 deg F for 28 days, followed by an additional 3
days in the moistroom with the surface of the slab covered with water % in. in depth.
These will be referred to hereafter as moist cured.
2. Continuously moist cured at 73 deg F for 14 days, then 14 days in the air of the
laboratory at 73 deg F and 50 percent relative humidity, followed by an additional 3
5 ■
cn
c
U
l/)
X3
CD
C
a
o
Scale Procedure No. 1
Non-Air-Entrained ^C^"
Moist -Cured AX'~\^^'^
^-2"
r~^7s^-^ %
i&z
"o% "
Scale Procedure No. 1
A /E Moist- Cured
ic£->
slZ
0% o,a
nd 5%^ ,
Scale Procedure No.l
NonVE Air- Dried
oW ^z-^ar.
iQ%
Scale Procedure No.l
A /e Air- Dried
t- Z t 4 and S %
Scale Procedure No. 2
Nion A /g. Moist -Cured
0%
Scale Procedure No. 2
A /E Moist -Cured
^^
£25
4% j
h%
/l&%
Sea
e Procedure No. Z
Non
a /e Air- Dried
I
/
o%
Scale
Proced
jre Na2
A /£
Air-
Dried
r
2%-\
.0%
lfc%^
J — ■ —
L 4 <wd 8 %
50 100 150 200 50 IOC 150
Number of Cycles of Scaling Test
Figure 4. Effect of scale test procedure, concentration of de-icer
and curing on the surface scaling of non- ai r -entrained and air-
entrained concretes. Curing: See Table 9 for details. De-icer:
Commercial flake CaC^. Aggregate: Elgin, Illinois sand and Eau
Claire, Wis. crushed gravel {1-in. top size). Cement Content: 6
sacks per cu yd. Slump: 2 to 3 in. Air Contents: Non-A E - 2.2
percent, A/E - 7.1 percent.
days in air with the surface of the slab covered with water % in. in depth. These will
be referred to hereafter as air dried.
Test Methods
Three different procedures were followed in determining the surface scaling result-
ing from the application of different de-
TABLE 1 icers:
CHEMICAL COMPOSITION OF . Procedure 1. After freezing 250 ml
TYPE I BLEND
PC A Lot No. 18681. Blend of equal parts
by weight of four Type I cements pur-
chased locally.
of water on the surface of a concrete slab
Major Components
%
SiOi
20.66
AlaOa
5.89
FeaOa
2.84
Total CaO
62.90
MgO
2.96
SO s
2.16
CT»
C
Ignition Loss
1.58
4-
Minor Components
%
Mn 3 3
0.28
So!
Free CaO
1.09
00 c
Insoluble Residue
0. 18
q
Alkalies:
ro 3
Na 2
0.20
.«
q5 w
K 2
0.54
E
Total as Na*0
0. 56
3
Z
b 8
i £
o
Hake Calcium Chloride
Z% Concentration, by wt
Thaw Solution Refrozen
^125 Cycles
50 Cycles
Air Content of Concrete - % (Pressure)
re 6. Effect of entrained air on re-
sistance to surface scaling (scale test
prodedure -gates: Elgin, 111.
sand and Lau Claire, His. gravel. Cement
Content: 6 sacks per cu yd. Slump: 3 in.
Curing: 14 days moist, 14 days in air plus
3 days in air *i th water on top surface.
Tra p Pock
Sand fr Stone
o Non A /fc Moist-Cured
• • m h Air-Dned
x A/ E Moist-Cured
A- - Air- Dried
Elg in Sand ^
Eau Claire Gravel
i
B B
o -
Non */fc
Moiet-Cxired]
Air -Dried
*
%
Moist Cured
A
Air-C
J
12 3 4
Numerical Scale Rating
Solution Replaced
Figure 5. Comparison of scale test pro-
cedures.
TABLE 2
POTENTIAL COMPOUND COMPOSITION
OF CEMENT
Compound
C3S
C*S
CsA
C«AF
CaSO«
Free CaO
% by Wt
44
8
25.
4
10.
8
8.
7
3.
67
1.
09
in a room maintained at -20 deg F, the
slab was removed to a room maintained
at 70 deg F and de-icer was applied im-
mediately to the ice. Alter thawing, the
resulting solution was removed, the sur-
face was rinsed and 250 ml of water was
placed on the surface for the next freeze
portion of the cycle. The total time in
freezer was approximately 18 hours. The
total time in the thawing room was ap-
proximately 6 hours.
Procedure 2. The same conditions
existed as in No. 1 except that the parti-
cular solution of de-icer and water was
kept on the specimen during both the
freeze and thaw portions of the cycle.
TABLE 3
MISCELLANEOUS PHYSICAL TESTS OF CEMENT
Tests made in accordance with ASTM Standards current in
December, 1951 (specific gravity determined in water rather
than kerosene).
Specific surface, sq cm per
gram
Wagner
1710
Blame
3310
Passing No. 325-mesh, %
91.1
Specific gravity, in water
3.182
Normal consistency, %
24.5
Time of setting: Vic at
Initial
3 hr 15 min
Final
6 hr 20 min
Gillmore
Initial
4 hr 20 min
Final
6 hr 30 min
Autoclave expansion, %
0.135
Air content, 1-4 standard mortar, %
8.2
TABLE 4
DATA ON AGGREGATES
Source and
Type
Fine Aggregate
Source and % Retained on Sieve Fine- Bulk 24-Hr Mean Linear
Type No. Indicated ness Sp Gr, Absorption, Thermal Coeff
1 S 16 30 50 IM Modulus S. S. D. a % by Wt of Expansion, b
xl0 9 /°F
Dresser, Wis
(crushed)
5
30
55
80 92 2.62 2.918
1. 14
4. 74
Elgin, 111.
(natural)
18
33
57
87 95 2.90 2.645
2.25
5.73
Coarse Aggregate
% Retained on Sieve
Indicated
1-in.
3/ .
A -in.
/fe-in.
No. 4
Bulk 24-Hr Mean Linear
Sp Gr, Absorption, Thermal Coeff
S. S. D. a % by Wt . of Expansion, b
Dresser, Wis
(crushed)
25
70
100
2. 980
0.20
4. 74
Eau Claire, Wis
(natural)
25
70
100
2. 693
1. 33
5.94
a Saturated, surface-dry.
b Dilatometer method.
TABLE 5
CONCRETE MDC DATA
Cement
Cement NetWC. % Slump Air
Content, gal. per Sand, in. Content, %
sacks per sack Abs (pressure)
cu yd Volume
Dresser,
Wis Fine and Coarse Aggregate (Crushed)
Type I
6. 7. 2 46 2. 2 2. 1
Type 1 +
Vinsol Resin
5. 8 6.9 42 3.0 7. 1
Elgin
111. Fine Aggregate and Eau Claire, Wis
Coarse Aggregate (Natural)
Type 1
6.0 5.2 41 3.2 2.2
Type I +
Vinsol Resin
6. 4. 8 36 3.3 7. 2
The sodium chloride, calcium chloride,
and urea solutions were replaced with
fresh solutions once each week. The
ethyl alcohol solutions were replaced
twice each week.
Procedure 3. In this procedure, the
specimen was frozen with the surface
damp (no excess water). On removal to
the thawing room, the surface was cov-
ered with 250 ml of solution containing
the particular amount and type of de-icer
required. After completion of thawing,
the solution was removed, and the surface
was rinsed and drained completely for the
next freeze portion of the cycle.
Scale Test
Specimens:
TABLE 6
RESULTS OF SCALING TESTS WITH DIFFERENT DE-ICERS
Thaw solution refrozen (Procedure 2)
3- by 6- by 15-in, slabs cured continuously moist for 31 days prior to start of test
Cement Content: 6 sacks per cu yd, 2\' 2 to 3Vin. slump
Aggregates: Elgin, Illinois sand and Eau Claire, Wisconsin gravel (1-in. top size)
Air Contents: Non-A E - 2.2%, A/E - 7. 4%
Concen-
tration
of Soln
after
Thawing,
%by Wt
Non-A
Numerical Scale Rating at
lr-Entrained Concrete
Ind
icated Number of Cycles
Air-Entrained Concrete
5 15
2b
50
75
100
150 200
5
15
25
50
7S
100
150
200
No De-icer
0+
1-
1 +
1 +
2- 2+
0+
0+
1-
Flake Calcium Chlon
de
2
4
8
16
1-
0+
u
1-
0+
4-
1+
1-
(70) a
3-
2-
0+
3.
2
1
(133)
3 4 +
3- (164)
0+
+
0+
1-
0+
0+
1
1
1-
0+
(150)
1+
1-
1-
Sodium Chlnririp
2
4
8
16
2
u
0+
(25)
4 +
0+
(35)
3-
1
4-
2-
5-
2
(108)
2, 3 +
o.
0+
1
0*
0-
u
0+
0+
3+
1
0+
5-
2
0+
Nrpa
2
4
8
16
0+
1-
0+
2
3
1-
0+
<50>
3-
1+
5-
2+
(85)
3-
(150)
0+
0+
+
1-
1-
0+
0+
1
1
1-
0+
2
2-
1 +
1-
4-
4-
2-
1-
Ethyl Alcohol
2
4
8
16
0+
(h
0+
G+
u
u
1
1
4
(50)
4~
3
(75)
(60)
4+
(85)
0+
0+
0+
0+
0+
0+
0+
0+
0+
1
1+
1-
0*
2+
3-
2-
1 +
3-
4-
3-
2
a ( ) - Number of cycles at which test was
discontinued at
a rating of 5,
The following listing shows which de-icers and which concretes were used in these
three procedures:
Procedure 1 - Calcium Chloride
Both aggregate combinations
Non-air-entrained and air-entrained
Both curing conditions
Procedure 2 - Calcium Chloride
Both aggregate combinations
air-entrained and air-entrained
Both curing conditions
Sodium Chloride, Urea, and Ethyl Alcohol
Elgin sand and Eau Claire gravel
Non-air-entrained and air-entrained
Moist-cured concretes only
Procedure 3 - Calcium Chloride
Dresser trap rock sand and coarse aggregate
Non-air-entrained
Both curing conditions
At intervals during the sealing test, the surfaces were examined carefully, rated as
to extent and depth of scale and assigned a numerical rating as follows: - no scaling,
1 - very slight scaling, 2 - slight to moderate scaling, 3 - moderate scaling, 4 - mod-
to severe scaling, and 5 - severe scaling.
TABLE 7
RB8ULT8 Of 84 AUNG rESTS TRAP ROCK FINE AND COARSE AGGREGATE
De-icer. Flake calcium chloride
i M 14 duy.s 3 daya in air with I
.mp
1L rgregate (1-in. top
1%
Nun*
i
2 2 (35)
i 13-;
3- (35)
f
1-2 4> (163)
2 o. I ISO) I (53)
4
! .50)
-
4- (63) 1 ► 4
Air-Entrained - Moist Cured
0* 0+ -
2 0000 0* 0* 1
'000
DO 000*1-1 2- 3 (188)
oooo o a*
000 O* 000000*1
000000
0> 0+ Q» 0* 0* 1- 1> 2-
Air-Entrained - Air Dried
2 00000 O* 0^00000000
000 000000000
I
t O* IV O* 00000000
-----
000 o oooooooo o b
i r which te
-d off abruptly . ;*. .
10
TABLE 8
RESULTS OF SCALING TESTS - ELGIN SAND AND EAU CLAIRE GRAVEL
Specimens: 3- by 6- by 15-in. slabs De-icer: Flake calcium chloride
Curing: (a) 31 days moist (b) 14 days moist, 14 days in air plus 3 days in air with water on
surface
Cement Content; 6 sacks per cu yd, 2- to 3-in. slump
Aggregates; Elgin, 111. sand and Eau Claire, vVis. crushed gravel (1-in. top size)
Air Content: Non-A/E - 2. 2%, A E - 7. 1%
Concen- ' ' "
tration
of Soln Numerical Scale Rating at Indicated Number of Cycles
Thawing Thaw Solution Replaced (Procedure 1) Thaw Solution Refrozen (Procedure 2)
% by Wt 5 15 25 50 75 100 150 200 5 15 25 50 75 100 150 200
Non-Air-Entrained - Moist Cur ed
1-1+ 2- 2 - . . ~ ~ I
2 0+2+3 4 5- 0+ 1+ 2- (40)
3 0+2-3- 4 5 _ .
4 1-3-3 4+ 5- 0+ 1- 1 + 4 (55)
6 0+0+3- 4- (138)* ......
8 0+0+23-4 5-0+ 1- 1+ 4+ (55)
10 1- 1-2+3- 4 5- - - - . . . .
16 1- 1- 2-2+ 3- 3 0+ 1- 2+ (72)
Non-Air-Entrained - Air Dried
00000 0+ 0+ ----- -
000 0+1-2-4+ (55)
4 0+1-2- (40)
J 0+ 0+ 0+ 0+ 0. 0+ 0+ 1- 2- 3+ 4- 4+ (125)
-i? 0+1-1-1-1- 1 1+00003-3+ (150)
„ Air-Entrained - Moist Cured
o oooooo 0+ "~ (^ 7Z I
0+000+0+1-1-2-3
3 000000 -
4 o 0+ i+ 2-
6 000000 0+ - -
® 0+1-1-1-12-
io oooooo o o -.:....
-i? 0+0+ 0+ 0+ 0+ Q+ Q+ 0+ Q i. i 2- 4- (163)
. Air-Entrained - Air Dried
0+0+ 0+ ~ol 7~.
oooooo 0+0+ 0. 0+ 0+ 0+ 0+ 0+
1 oooooo ooooooooo
x * oooooo o ooooooooo
-£ 0- °^ CW + 0+ Q, (K O+OOOooo Q Qb
Number of cycles at which test was discontinued at a rating of 5
.* Surface shell scaled off, about V^-jn. thick. Discontinued at 237 cycles.
11
RESULTS OF SCALING TESTS - TRAP ROCK FINE AND
COARSE AGGREGATES
Test Cvcle: Slabs frozen with surface damp (no excess of
water). Thaw solution placed directly on surface at start
of thawing period (Procedure 3).
Specimens: 3- by 6- by 15-in. slabs. De-icer. Flake calcium
chloride.
Curing: (a) 31 days moist (b) 14 days moist, 14 days in air
plus 3 days in air with water on surface.
Cement Content 6 sacks per cu yd, 2- to 3-in. slump, non-
air-entrained.
Aggregates: Dresser, Wisconsin, trap rock fine and coarse
aggregates (1-in. top size).
Air Content: 2. 1%
DISCUSSION OF RESULTS
Effect of Concentration of Different De-
Icers on Scale Resistance
Conceotratioi
ai Thaw
Numerical Scale Rating at Indicated
Solution
Number of Cycles
% by Wt
25
50 75
100
150 25 50 75
100
150
2
0*
0+ 0+
0+
0+000
4
U*
0+ 0+
0+
0+000
6
U
12
16
00
The work of Arnfelt ' has indicated
that concretes frozen and thawed while im-
mersed in solutions of different materials
showed maximum deterioration at rela-
tively low solution concentrations and that
further increase in concentration resulted
in a decrease in deterioration. Field ob-
servations in this country appeared to in-
dicate that scaling of concrete pavements
increased with increase in the amount of
calcium chloride or rock salt used as de-
icers.
Before making a general attack on the
problem of surface scaling, it was desir-
able to substantiate Arnfelt' s work using
four materials as de-icers: calcium chloride, sodium chloride, urea, and ethyl alcohol.
The concretes used in this portion of the study were made with the Elgin sand and Eau
Claire gravel. Further information on these concretes is shown in Table 5.
These concretes were moist cured prior to test. Scale test Procedure 2 was used
to simulate in some respects Arnfelt' s tests in which the concretes were frozen and
thawed while immersed in the solution. In Procedure 2, the solution of water and de-
icer remained on the surface of the specimen during both the freeze and thaw portions
of the cycle.
Table 6 and Figure 1 show the effect of concentration of solution on the scale resis-
tance of these concretes. The non-air-entrained concretes show severe scaling much
sooner than the air-entrained concretes, with the rate of scaling much greater at solu-
tion concentrations of 2 and 4 percent than at 0, 8, and 16 percent. These data confirm
the observations of Arnfelt. Figure 2 shows more clearly the greater amounts of sur-
face scaling occurring with the intermediate and relatively low concentrations of de-
icers.
These data are important with regard to the mechanism by which scaling occurs.
The opinion advanced most frequently is that the mechanism is primarily a chemical
attack. If this were true, surface scaling would be expected to increase with an in-
crease in concentration of de-icer. These tests show that this is not so. In addition,
the de-icers used in these tests are dissimilar chemically. It appears, therefore, that
the mechanism producing surface scaling is primarily physical.
Effect of Test Procedure on Scale
Resistance
Tables 7 and 8 show the results of
scaling tests of non-air-entrained and
air-entrained concretes made with the
Dresser trap rock aggregate and the El-
gin sand and Eau Claire gravel, using
both Procedure 1 and 2 and calcium chlo-
ride as the de-icer. In Procedure 1 the
thaw solution is replaced with fresh water
for the freeze portion of the cycle; in Pro-
RESULTS OF SCALING TESTS - ELGIN SAND AND
EAU CLAIRE GRAVEL
Scale Test: Thaw solution refrozen (Procedure 2).
De-icer Flake calcium chloride, 2% ^jlution concentration
(by weight).
Specimens: 3- by 6- by 15-in. slabs cured 14 days moist, 14
days in air plus 3 days in air with water on surface.
Cement Content: 6 sacks per cu yd, 3-in. slump.
Aggregates: Elgin, Illinois sand and Eau Claire, Wisconsin
gravel (1-in. top size).
Air Content: Agent added at mixer to produce range in air
contents shown.
1 "Damage on Concrete Pavements by
Wintertime Salt Treatment," Arnfelt,
Harry, Meddelande 66, Statens Vaginstitut,
Stockholm, 1943.
Air Content
Numerical Scs
le Rating at Indicated
of Concrete
Number of
Cycles
%
5
15
25
50
75 100 125
2.3
1-
1
2-
2+
3+ 3+ 4-
3.2
0+
0+
0+
0+
1- 1- 1-
4. 7
0+
0+
0+
0+
0+0+ 0+
6.2
0+
0+
0+ 0+ 0+
7.5
0+0+0+
9.9
0+
0+
0+0+0+
12
cedure 2 the thaw solution is refrozen. Companion concretes were cured continuously
moist or moist plus a period of air drying prior to test.
Figures 3 and 4 show the numerical scale ratings as a function of the calcium chlo-
ride solution concentration for these concretes and test procedures during 200 cycles
of test. Where scaling has developed, note that, in general, the more severe scaling
occurs at some intermediate and relatively low solution concentration. The scaling
which occurs when the thaw solution is refrozen is generally more severe than when
the solution is replaced. The usual laboratory procedure of replacing the thaw solution
with fresh water (Procedure 1) apparently does not represent the most severe exposure
attainable. For the purpose of determining the scale resistance for the most severe
exposure conditions, the laboratory test should involve refreezing the thaw solution
(Procedure 2). There appears to be no general relationship between the scaling pro-
duced by Procedures 1 and 2. Figure 5 shows only that Procedure 2 is generally much
more severe than Procedure 1.
Some non-air-entrained concretes, both moist cured and air dried, made with the
Dresser trap rock aggregate were tested for scale resistance using Procedure 3. The
results are shown in Table 9. In test Procedure 3 the concrete specimen is frozen with
the surface damp (no excess water) and the surface is then thawed with the appropriate
calcium chloride solution. The scale ratings obtained during 150 cycles of test are
shown in Table 9. No scaling has developed on any of these concretes exposed to cal-
cium chloride solutions concentrations ranging from to 16 percent, except for some
very slight scale on the moist cured concretes exposed to the 2 and 4 percent solution
concentrations. These very same concretes would have scaled rapidly under the test
conditions of Procedure 1 and 2. It would appear that the scale resistance of the sur-
face was enhanced by the rapid drying of the top surface of the slab, such as would oc-
cur when a warm wet specimen is placed in cold atmosphere having a low moisture
content.
Effect of Prior Curing on Scale Resistance
Pavements rarely obtain curing comparable to continuous moist curing in the labora-
tory. Generally, after a minimum prescribed curing period, the concrete is exposed
to drying conditions with subsequent rewetting at intervals by rainfall. On rewetting,
however, the amount of water reabsorbed rarely equals that lost during the drying
period, unless the period of wetting is exceptionally long. This results in a lowered
degree of saturation.
The effect on scale resistance of continuous moist curing and a curing period com-
prised of both moist curing and air drying is shown in Figures 3 and 4. In almost all
instances, continuous moist curing resulted in concrete surfaces less resistant to sur-
face scaling than the concretes which underwent some air drying prior to test. For the
non-air-entrained concretes, although the period of air drying reduced the amount of
scaling, the resistance of the surfaces was not satisfactory, with the exception of the
air-dried concrete made with the Eau Claire aggregate which was tested for scale re-
sistance by Procedure 1, replacing the thaw solution with fresh water.
The air-dried air-entrained concretes made with both combinations of aggregates
showed only very slight scaling during 200 cycles of Procedure 1 or 2. Despite the
severity of Procedure 2, the period of air drying of the air-entrained concrete's pro-
duced concretes resistant to 200 cycles of this test procedure. Concrete pavements
may sometimes be subjected simultaneously to conditions of exposure similar to that of
Procedure 2 and to low de-icer concentrations. Despite this particularly severe com-
bination of exposure conditions, air-entrained concrete pavements have an excellent
performance record, which may in part be the result of periodic air drying of the pave-
ment surface. Laboratory tests should therefore include tests on air-dried concretes.
Effect of Amount of Air on Scale Resistance
From over-all durability considerations, the desired air content for concretes made
with aggregate of 1-in. maximum size is in the range of 4 to 7 percent based on pi ■
vious laboratory tests and field experience. The air-entrained concretes used in this
13
study had air contents near the upper limit of this range, since preliminary tests had
indicated that a combination of continuous moist curing followed by exposure to low de-
icer concentrations in scale test Procedure 2 (thaw solution refrozen) was an extremely
severe test. Additional concretes were prepared in order to evaluate the scale resis-
tance at various air contents within this range. Figure 6 shows some of these data
which indicate that the concretes with 4. 7 percent air content showed surface scale
ranging from none to very slight as evidenced by a scale rating of 0+ at 125 cycles.
For concretes cured and tested in the same manner (see Table 8) and made with the
same aggregate and an air content of 7. 1 percent, the scale rating at 125 cycles was
identical. This indicates that an air content at the middle of the recommended range of
4 to 7 percent for this type of concrete performed as well as the concrete with 7. 1 per-
cent air content. Further details of these tests are shown in Table 10.
SUMMARY AND CONCLUSIONS
These laboratory tests provide new information on the effect of de-icers on the sur-
face scaling of non-air-entrained and air-entrained concretes, each made with two dif-
ferent coarse aggregates, cured differently, and tested under a variety of scale test
procedures. While these tests did not provide data from which a complete concept of
the mechanism involved can be drawn, they have provided a basis for further study,
some of which is already under way.
Based on these laboratory tests, the following statements appear valid:
1. Chemically dissimilar materials, inorganic or organic, salts or non-salts, which
function as de-icers also cause "salt" scaling, which more appropriately should be
called "de-icer scaling. "
2. Relatively low concentrations (of the order of 2 to 4 percent by weight) of de-icer
produce more surface scaling than higher concentrations or the absence of de-icer.
3. On the basis of the foregoing, it appears that the mechanism of surface scaling
is primarily physical rather than chemical.
4. Surface scale test procedures greatly influence the rate of scaling. The
most severe test procedure yet discovered is one in which the concrete is alternately
frozen and thawed with the de-icer solution remaining on the top surface of the concrete
rather than being replaced with fresh water prior to each freezing.
5. No scaling was produced when the concrete surface had no free water on it during
the freeze portion of the cycle.
6. A period of air drying of the concretes prior to the start of scaling tests in-
creased the resistance to surface scaling. Air-entrained concretes treated in this
manner were immune to the most severe scale test procedure for more than 200 cycles
of test.
7. With the fixed cement content and slump as specified by these tests, the concrete
made with the Elgin sand and Eau Claire gravel showed more resistance to surface
scaling than the concretes made with the Dresser trap rock fine and coarse aggregate.
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